Polypropylene resin compositions are in use for automotive interior or exterior parts, electric parts, etc. because they are materials generally being excellent in rigidity, impact resistance, etc.
Patent document 1 discloses a polypropylene resin composition developed for the purpose of improving molding processability, mechanical strength balance, and paintability which is a composition composed of a propylene-ethylene block copolymer, an ethylene-α-olefin copolymer rubber, and an inorganic filler, wherein the propylene-ethylene block copolymer component is composed of a propylene homopolymer portion, a propylene-ethylene random copolymer portion, and an ethylene homopolymer portion, and the propylene-ethylene random copolymer portion has a number average molecular weight of 20×104 or more and a weight average molecular weight of 60×104 or more.
Patent document 2 discloses a polypropylene resin composition developed for the purpose of improving rigidity, heat resistance, hardness, moldability, impact resistance, and surface gloss of a molded article, the polypropylene resin composition being composed of a propylene polymer having a melt flow rate of 10 to 400 g/10 minutes and containing 0.1 to 20% by weight of a component soluble in n-decane at room temperature, wherein the component soluble in n-decane at room temperature has an intrinsic viscosity of 0.2 to 10 dl/g and a component insoluble in n-decane at room temperature has a pentad isotacticity of 0.95 or more, a propylene-ethylene random copolymer containing 50 to 90 mol % of units derived from propylene and having an intrinsic viscosity of 1 to 4 dl/g and a molecular weight distribution Mw/Mn of 1.5 to 3.5, an ethylene-α-olefin copolymer containing 50 mol % or more of units derived from ethylene, and an inorganic filler.
Patent document 3 discloses a polypropylene composition developed for the purpose of improving moldability, rigidity, hardness, impact resistance, and balance therebetween of automotive parts, the polypropylene composition comprising 60 to 72% by weight of a propylene-ethylene block copolymer, 11 to 19% by weight of an ethylene-octene copolymer, and 17 to 23% by weight of talc, wherein the propylene-ethylene block copolymer portion contains a component insoluble in xylene at room temperature, the insoluble component having a steroregularity index of 98.0 mol % or more measured by 13C-NMR, the content of ethylene units in the insoluble component being 2% by weight or less, and the propylene-ethylene block copolymer portion contains 15 to 26% by weight of a component soluble in xylene at room temperature, the content of ethylene units in the soluble component being 50 to 85% by weight, the ash content being 16 to 23% by weight, the melt index (measured at 230° C. and 2.16 kgf) being 25 g/10 min or more, the Rockwell hardness being 70 or more, and the Izod impact strength being 450 J/m or more.